In order to reduce the landing distance of a jet engine powered aircraft, as well as to increase the margin of safety when the aircraft is landing on a wet or icy runway, thrust reversers are utilized on the jet engines in order to provide a braking thrust for the aircraft. Typically, such thrust reversers are formed by thrust reverser "doors" which are capable of pivoting between two positions about an axis which is transverse and substantially diametrical with respect to the jet of the engine.
The first position finds the doors in a stowed position, out of the direct path of the exhaust blast of the engine. In this position, the doors form the exhaust nozzle of the gas turbine engine so that the thrust of the engine is directly rearward, thereby producing the forward thrust of the aircraft. In the second position, the doors are pivoted about the pivot axis to a transverse, blast deflecting or deployed position, to intercept and redirect the jet blast and produce the braking thrust for the aircraft when needed. In such thrust reversers, the trailing edge of the reverser doors must be fully scarfed to enable the deployment of the doors and the butting of the trailing edges of the two doors against one another in the deployed position. This scarfing produces what is known as a "fishmouth" shape at the exhaust outlet because of its appearance when viewed from the side.
The prior art demonstrates some variable area exhaust nozzles for thrust reversers, and such devices are shown in U.S. Pat. No. 4,966,327 and French Patent 2,614,939. Theoretically, a variable area exhaust provides certain benefits for the jet engines, in enabling them to adapt to different conditions of the flight. For example, different characteristics of the engines are desirable for take off, climb and cruise modes of operation, and varying the exhaust area enables the engine to better achieve the optimum characteristics.
According to the prior patents mentioned above which integrate a variable exhaust area nozzle with the thrust reverser, the thrust reverser doors do not (and cannot) in any of the controllable positions of the reverser doors define the throat of the exhaust nozzle to be at the trailing edge of the nozzle/reverser doors. In these prior patents, the inner flow line of the thrust reverser doors is convergent to the throat, with a cylindrical extension aft of the throat. This means that at any position of the thrust reverser nozzle, the throat of the nozzle always remains significantly upstream of the reverser nozzle trailing edge. This is an inherent characteristic in the design of the prior art as it is described in French patent 2,382,594.
In the case of the prior art thrust reversers using the scarfed or fishmouth nozzles, another drawback arises in that the performance characteristics of the engine are somewhat degraded such that varying the exhaust area merely helps to recapture the efficiency lost to the scarfing. This degradation of performance is caused by a not-insignificant lateral efflux of exhaust gas in the area of the cutouts.
In U.S. Pat. Nos. 4,194,692 and 4,093,122, the thrust reverser doors are incapable of defining, in any of their controllable positions, the throat area of the nozzle. By the term "throat" as it is commonly used in this field is meant the point or location of the minimum cross-sectional area of the engine's ejection nozzle. In both of these prior patents, the throat area of the nozzle is not adjusted by the thrust reverser doors, but rather by a separate variable convergent nozzle.
Accordingly, a primary object of the present invention is to provide a thrust reverser which overcomes the aforementioned disadvantages of prior art thrust reversers.
A further object of the invention is to provide an improved thrust reverser which integrates a variable area exhaust nozzle.
Still another object of the invention is to provide a thrust reverser having a variable area exhaust nozzle and a planar exhaust nozzle, eliminating the scarfed or fishmouth configuration of prior thrust reverser doors.
Yet another object of the invention is to provide a thrust reverser in which variation in the area of the exhaust throat takes place at the trailing edge of the planar nozzle.
Still a further object of the invention is to provide a thrust reverser construction wherein the the reverser doors are the operating means for the exhaust nozzle in order to optimize the engine operating characteristics for different phases of the flight.
These and other objects and advantages of this invention will become apparent from a consideration of the following description of the invention.